RESUMO
We previously reported the dinuclear material [Fe(II) (2)(ddpp)(2)(NCS)(4)] x 4 CH(2)Cl(2) (1 x 4 CH(2)Cl(2); ddpp = 2,5-di(2',2''-dipyridylamino)pyridine) and its partially desolvated analogue (1 x CH(2)Cl(2)), which undergo two- and one-step spin-crossover (SCO) transitions, respectively. Here, we manipulate the type and degree of solvation in this system and find that either a one- or two-step spin transition can be specifically targeted. The chloroform clathrate 1 x 4 CHCl(3) undergoes a relatively abrupt one-step SCO, in which the two equivalent Fe(II) sites within the dinuclear molecule crossover simultaneously. Partial desolvation of 1 x 4 CHCl(3) to form 1 x 3 CHCl(3) and 1 x CHCl(3) occurs through single-crystal-to-single-crystal processes (monoclinic C2/c to P2(1)/n to P2(1)/n) in which the two equivalent Fe(II) sites become inequivalent sites within the dinuclear molecule of each phase. Both 1 x 3 CHCl(3) and 1 x CHCl(3) undergo one-step spin transitions, with the former having a significantly higher SCO temperature than 1 x 4 CHCl(3) and the latter, and each has a broader SCO transition than 1 x 4 CHCl(3), attributable to the overlap of two SCO steps in each case. Further magnetic manipulation can be carried out on these materials through reversibly resolvating the partially desolvated material with chloroform to produce the original one-step SCO, or with dichloromethane to produce a two-step SCO reminiscent of that seen for 1 x 4 CH(2)Cl(2). Furthermore, we investigate the light-induced excited spin state trapping (LIESST) effect on 1 x 4 CH(2)Cl(2) and 1 x CH(2)Cl(2) and observe partial LIESST activity for the former and no activity for the latter.
RESUMO
A dinuclear iron(II) complex containing the new pyridyl bridging ligand, 2,5-di(2',2''-dipyridylamino)pyridine (ddpp) has been synthesised and characterised by single-crystal X-ray diffraction, magnetic susceptibility and Mössbauer spectral methods. This compound, [Fe(2)(ddpp)(2)(NCS)(4)]4 CH(2)Cl(2), undergoes a two-step full spin crossover. Structural analysis at each of the three plateau temperatures has revealed a dinuclear molecule with spin states HS-HS, HS-LS and LS-LS (HS: high spin, LS: low spin) for the two iron(II) centres. This is the first time that resolution of the metal centres in a HS-LS ordered state has been achieved in a two-step dinuclear iron(II) spin-crossover compound. Thermogravimetric data show that the dichloromethane solvate molecules can be removed in two distinct steps at 120 degrees C and 200 degrees C. The partially de-solvated clathrate, [Fe(2)(ddpp)(2)(NCS)(4)]CH(2)Cl(2), undergoes a one-step transition with an increased transition temperature with respect to the as synthesised material. Structural characterisation of this material reveals subtle changes to the coordination geometries at each of the iron(II) centres and striking changes to the local environment of the dinuclear complex. The fully de-solvated material remains high spin over all temperatures. Interestingly, the solvent can be re-introduced into the monosolvated solid to achieve complete conversion back to the original two-step crossover material, [Fe(2)(ddpp)(2)(NCS)(4)]4 CH(2)Cl(2).